1. Field of the Invention
The present invention relates generally to an antenna device and an electronic device for wireless communication including the same.
2. Background of the Invention
Electronic devices for wireless communication have become important electronic devices for everyday life. In particular, terminals such as smartphones having improved communication speed and data processing speed and providing a user assistance function in addition to a web surfing function have recently become mainstream electronic devices for wireless communication.
Electronic devices for wireless communication are necessarily provided with antenna devices for performing wireless communication. Early antennas such as helical antennas that protruded from electronic devices have been improved and replaced by built-in antennas in order to prevent damage to the antennas and improve portability of electronic devices.
In general, Planar Inverted-F Antennas (PIFAs) having one feeding portion and one ground portion have been used as built-in antennas that support multiple bands. For example, such built-in antennas have been designed to cover antenna bands such as GSM900, DCS1800, PCS1900 and Wideband Code Division Multiple Access (WCDMA) band 1.
According to a Code Division Multiple Access (CDMA), Global System for Mobile communication (GSM) or WCDMA technology, three or four frequency bands are generally used. For example, it is satisfactory for antennas installed in most WCDMA terminals to support a frequency of 2100 MHz band (as a representative exception, antennas for WCDMA for North America should support a frequency of 850 MHz/1900 MHz). However, according to a Long Term Evolution (LTE) technology and other communication technologies developed thereafter, various frequency bands are used for wireless communication in different nations/regions. For example, in China where an LTE Time-Division Duplex (TDD) technology is used, frequency bands corresponding to band 38 (2600 MHz), band 39 (1900 MHz) and band 40 (2300 MHz) are used for wireless communication.
In general, a built-in antenna of an electronic device implements a target frequency band by means of low-frequency band resonance induced according to an antenna length, secondary resonance of the antenna length, and high-frequency resonance induced using a branch pattern connected or coupled to a main pattern. A high-frequency band is a currently important communication band, and is continuously extended upwards. However, inducing resonance is limited at some frequency bands due to limitation in space for implementing an antenna (e.g. branch) pattern.
FIG. 1A illustrates resonance of a monopole antenna designed on a theoretically infinite ground.
Referring to FIG. 1A, resonance f0 and secondary resonance f1 are induced according to a physical length of the monopole antenna. The frequency f1 is three times the frequency f0, i.e., f1=3f0.
FIG. 1B illustrates typical antenna resonance induced in a mobile terminal. In this case, conditions for an internal path and a ground structure on a Printed Circuit Board (PCB) are compensated so that a secondary resonance frequency f1′ is approximately two times a primary resonance frequency f0′. Provided that the primary resonance frequency f0′ is 900 MHz-1 GHz, the frequency f1′ in a terminal is approximately 1.8 GHz-2 GHz which corresponds to a communication frequency domain currently and generally used.
However, a high-frequency band that is currently and commercially used is extended up to 2.7 GHz, and it is necessary to use an additional branch pattern or modify a ground of a lower end portion of an antenna in order to secure a frequency band of at least 2 GHz. However, inducing resonance at a target frequency is limited due to various conditions. Furthermore, if an additional pattern is added, radiation performance may be degraded due to an insufficient space for mounding an antenna.